The background of the invention will be set forth in two parts.
1. Field of the Invention
This invention relates to an electromagnetic wave propagating device and more particularly to a microwave 180.degree. 3 db hybrid coupler utilizing slot line and microstrip techniques.
2. Description of the Prior Art
Microwave devices known as hybrids or hybrid junctions have been in use for many years. Hybrids are four-port devices which, relative to one port chosen as the input, produce one isolated port and two coupled ports. Many of these hybrids have used hollow waveguide, and others have used microwave integrated circuit techniques. One such device used in integrated circuit applications is a branch line coupler. This device uses differential electrical line lengths to produce the required signals at the output ports. For isolation, two equal amplitude signals are phased 180.degree. apart by differential line lengths which are then summed at its isolation port. The relative phase difference between its two coupled ports is 90.degree.. In this type of device, the differential electrical length varies with frequency, therefore so does the isolation and the relative phase of its coupled ports.
Another example of a prior art device of this type is the 3 db reverse coupler, which has two lengths of line coupled to each other over a quarter wavelength. The coupling and isolation are a function of the electrical length of this coupled section, making it frequency sensitive.
It should therefore be evident that an integrated circuit-type hybrid coupler that does not utilize differential lengths of line to achieve isolation or coupling because it has a natural isolation between its input and output ports, would constitute a significant advancement of the art.